Accident Board Findings

The final accident report issued by the Portuguese accident investigation authority did not identify a specific probable cause of the Air Transat Flight TSC236 accident. It did identify 12 findings as to causes and contributing factors, 18 findings as to risk, and 7 other findings. A summary of the significant findings from each category follows:

Findings as to Causes and Contributing Factors

Cause of the Fuel Leak

  • The replacement engine was received in an unexpected pre-service bulletin configuration to which the operator had not previously been exposed.
  • Neither the engine-receipt nor the engine-change planning process identified the differences in configuration between the engine being removed and the engine being installed.
  • The lead technician relied on verbal advice during the engine change procedure rather than acquiring the relevant service bulletin, which was necessary to properly complete the installation.
  • Although a clearance between the fuel tube and hydraulic tube was achieved during installation by applying some force, the pressurization of the hydraulic line during operation forced the hydraulic tube back to its natural position and eliminated the clearance.

Detecting the Fuel Leak

  • The flight crew did not detect that a fuel problem existed until the fuel imbalance advisory message was displayed and the fuel imbalance was noted on the Fuel ECAM page.
  • The crew did not correctly evaluate the situation before taking action.
  • The flight crew carried out the fuel imbalance procedure from memory, which resulted in fuel from the left tanks being fed to the leak in the right engine.
  • Conducting the fuel imbalance procedure by memory resulted in the crew not seeing the Caution note in the fuel imbalance checklist that may have led them to considering the fuel leak procedure in a timely manner.
  • Although there were a number of other indications that a significant fuel loss was occurring, the crew did not conclude that a fuel leak situation existed. Not conducting the fuel leak procedure was the key factor that led to the fuel exhaustion.

Findings as to Risk

Engine Change

  • The carry forward items list that accompanied the replacement engine listed a post modification hydraulic pump model, whereas the pre-mod fuel and hydraulic tubes installed on the engine required a pre-mod hydraulic pump.
  • The post-installation quality control checks following the engine change did not specifically require checking the installation of the hydraulic pump, hydraulic tube and the fuel tube.
  • In the absence of a requirement to conduct a pre-installation, service bulletin completion check, there is a risk that incompatible components may be installed on aircraft and not be detected by existing maintenance planning processes.

Fuel Leak Indications

  • The final forward transfer of the 3,200 kg of fuel in the trim tank resulted in this fuel feeding the leak in the right engine and delaying the annunciation of the fuel imbalance advisory message by 15 minutes.
  • There was not a clear, unambiguous indication or warning that a critical fuel leak existed.
  • The seriousness of a fuel imbalance caused by a fuel leak is undermined by the fact that such a situation only results in an advisory message, which does not require immediate flight crew action.

Operational Factors

  • The flight crew had never experienced a fuel leak during operations or training, which contributed to their not being able to conclude that a fuel leak existed.
  • The lack of training in the flight deck indications associated with a fuel leak resulted in this crew not being adequately prepared for the situation when encountered on the occurrence flight.
  • The Captain's skill in conducting the engines-out glide to a successful landing averted a catastrophic accident and saved the lives of the passengers and crew.

Other Findings

  • The unusual oil parameters on the right engine were the result of the high fuel-flow rate through the fuel/oil heat exchanger after the leak commenced.
  • The risk associated with the application of force while installing mixed-construction lines is not well known in the maintenance community, and is not covered in the training of maintenance technicians.

The complete list of the accident report findings may be read by clicking on the following link: Accident Report Findings

The complete accident report may be read by clicking on the following link: Air Transat A330 Final Report

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